Ammonium-phosphate fertilizer composition and method of making the same



Dec. 16, 1930. G. H. BUCHANAN AMMONIUM PHOSPHATE FERTILIZER COMPOSITION AND METHOD OF MAKING THE SAME Filed Jan.

quY H. WcHANAN.

INVENTOR ATTORNEY Patented Dec. 16, 1930 UNITED STATES P TEN OFFICE GUY H. BUCHANAN, 0F WESTFIELID, NEW JERSEY, ABSIGNOR 1'0 AMERICAN CYANA-. MID COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE.

ammomum-rnosrna'm rnarnrzna comros'rrronann' reason or Maxine 'rnn.

' su y Y Application filed January 28, 1927. Serial Io. 184,345.

This invention relates to fertilizers, more particularly to concentrated fertilizers of the ammonium phosphate type. The fertilizing value of ammonium phosphate has long been recognized and'many tons of commercial mono-ammonium phosphate are consumed in the fertilizer industry annually. Pure mono-ammonium phosphate contains 14.8% ammonia and 61.7% P 0 but the ordinary fertilizer grade of ammonium phosphate usually contams about 13% NIL and'about 48% P 0 In such material the ratio of ammonia to P 0 is about 1 to 3.7. While this ratio is satisfactoryfor certain types of crop, there are others where a higher ratio of-ammonia to P 0, is desirable, consequently there is a demand for an ammonium phosphate contain-,

ing a higher percentage of ammonia than the ordinary mono-ammonium salt.

Of the three hydrogen atoms of ortho phosphoric acid, the first exhibits the characteristics ofla stron acid and yields a salt of satisfactory stability. The second hydrogen atom of phosphoric acid is considerably weaker and, when neutralized with ammonia, the ammoniais held more loosely than is the ammonia combined with the first hydrogen.

However, this combination is still sufiiciently stable to permit the manufacture, shipment and use in the fertilizer indust of diammoniumphosphate. This is evi enced by experiments which I have conducted in which I have found that di-ammonium phosphosphate isnot suited for use in fertilizer manufacture owing to the ease with which it loses ammonia.

Some years ago a method was developed for the manufacture of di-ammonium'phosphate on which patent ap lication has beenfiled by me in the United tates' Patent Office, Serial No. 720,566, dated June 17,1924. This process relates to the production of the salt by a crystallization process, and works particularl well when reasonably pure phosphoric ad is available. If, however, the

phosphoric acid contains substantial amounts of iron or of aluminum, as is the case with phosphoric acid produced by the acidulation of phosphate rock with sul huric acid, the operation becomes considera ily more diflicult. Owingto the fact. that solutions of di-am- 'monium hosphate lose ammonia when concentrate it is necessary .to recover the diammonium phosphate by crystallization, and unless the precipitates of iron and aluminum are previousl removed, the recovery of the crystalline sa t is difiicult. The removal of theseprecipitated iron and aluminum phosphates by filtration or other mechanical means, before crystallization, although feasible, is diflicult owing to the gelatinous nature of the precipitates. 'In addition these precipitates contain hosphoric acid which is available as lant ood, so that if the diammonium p sphate is intended for fer-1 tilizer mixtures the removal of these phos phates lowers the phosphate recovery and consequently adds to the cost of manufacture of the product. I

Commercial practice in the manufacture of'mon'o-ammonium phosphate from crude phosphoric acid usually follows the cedure disclosed by Washburn in his United States Patents Nos. 1,142,068, 1,103,115 and 1,100,638, whereby the phosphoric acid is ammoniated only to the mono-state and the resulting solution, cbntaining the iron and aluminum phosphates in suspension, is evap orated to dryness. The process of manufacture according to these patents-is simple and the engineering problems are thorogghly worked out; thousands of tonsof p are so manufactured annuall Recognizing the desi-rabihty of an ammonia content higher than 13% ammonia, and at the same time desiring to retain the advantages of operation according to the above named processes, I attempted. to produce material of higher ammonia content by substantially the same procedure. It would naturally occur to one that di-ammonium phosphate could be produced by ammoniating the phosphoric acid tothe di-stage, instead of to the mono-stage as is 'done in the manuuct facture .of mono-ammonium phosphate, and

then evaporate to dryness in-exactly the same manner as in the manufacture of the mono- 'salt. I found, however, that when this procedure was followed the second ammonia was lost in the drying operation and that theprodnot delivered from the dryers was of almost the same composition as that obtained when the ammoniation was carried only to the monostage. It thus became evident that a diammonium compound, or, in fact any compound containing substantially more ammonia than the mono-salt could not be produced economically by these. older processes.

It next occurred to me that it might be possible to produce a material of higher ammonia content by ammoniating substantially dry mono-ammonium phosphate, for examle as produced by the process of Washburn, in solid form. To test this out I placed 100 grams of fertilizer grade mono-ammonium greater than the ratio for di'-ammonium phosphate and it was not at first apparent ]ust why the product was not more stable. Further examination showed that theinstability was due to the fact that the outside of the particles had been largely converted to triammonium phosphate, while the center of the particles contained unaltered mono-ammonium phosphate. In other words, the distributio n of t e ammonia upon the granules was not uniform.

I next found that if I stored this material in a closed container for a few hours, for example over night, it lost its ammonia odor although its ammonia content by analysis remained constant. .The explanation which I advance for this is that, during the time of storage, the ammonia was enabled to disperse itself uniformly throughout the granules, roducing di-ammonium phosphate throug out the entire mixture, the trl-ammonium phosphate on the outside of the particles yielding its excess ammonia. to the mono-ammonium phosphate on the inside of the granules. I found also that I could accelerate the uniform distribution of this ammonia by heating the mixture also that the absorption of the ammonia in the first instance was greatly accelerated by heating the mixture, and in my proceEs therefore prefer to conduct. the absorption operation at temperatures above atmospheric, say in the neighborhood' of 100 C. By so conducting the operation I not only speed up the rate of the chemical reaction, but I also minimize formation of tri-ammonium phosphate. I have also found that I can eliminate any last traces of tri-ammonium phosphate or of free ammoniafrom my product by evacuating the vessel in which the ammoniation or storage of the material takes place, the operation being preferably performed at temperatures above atmospheric.

In the accompanying drawing constituting a part hereof, the single figure is a vertical cross-sectional View of an apparatus adapted for the operation of my invention.

A cylindrical steel vessel 1 is provided with a jacket 2 into which steam from a source 3 is introduced, if necessary, in order to secure the desired temperature on the inside of the jacket, the jacket being provided with an outlet 4 for condensed steam, and the vessel having man-holes 5 for charging and discharging material 6.

An inlet 7 for ammonia gas leads into the vessel 1, which is connected to a source of Vacuum 8. A stirrer 9 rotated thru pulley 10 provides means for agitating the contents of vessel 1. In conducting the operation I charge into the shell of the vessel 1 monoammonium phosphate in the dry state, for example the product produced by the process of Washburn. I then cause the stirrer 9 to rotate and introduce ammonia gas into the Vessel through the inlet 7. Absorption takes place and the introduction of ammonia is continued until an amount has been added estimated to be substantially the amount required for the production of di-ammonium phosphate. The mixture heats up very rapidly at first, but as the operation is continued the temperature tends to fall and I sometimes find it desirable to maintain the temperature of the mixture by supplyin heatto the jacket 2 of the reaction vessel i introducing steam at 3. In order to speed up the reaction I ma sup ly the ammonia under pressures hig 1er tl fan atmospheric, for example, at about 60 pounds pressure.

When the required amount of ammonia has been added, I discontinue the addition of ammonia but allow the stirrer to rotate for several hours or at least until the reaction is complete. Finally I may exhaust the air and residual gases from the reaction vessel by use of a' vacuum pump in order to remove the last traces of. ammonia, both free'ammonia and ammonia combined as *tri-ammonium tus and ag the product for shipment. In physical appearance the ammoniated product resembles the'original ammonium phosphate very closely but its ammonia content has been increased. The composition is in the form of a porous granular mass substantlally dry to the touch and physically phosphate. I then open the apparaphosphate is the starting'material' the final product analyzes about 25% ammonia' and about 5.0% P 0 One of the important advantages of my.

process is the flexibility it imparts to the manufacture of fertilizers. Where mono and di-ammonium phosphates are produced by entirely distinct operations it is necessary to stock both materialsand it will frequently result that the demands, of the market will result in depletion of the stock of one of these materials while the 'second material is available in large volume. According to my process it is only necessary to produce and stock mono-ammonium phosphate. This may either be shipped out as such or ma be converted on a few hours notice to ieanimonium phosphate as required.

In the claims I have referred to substantially dr mono-ammonium phosphate. .By substantially dry mono-ammonium phosphate I mean material sufliciently dry so that it will not become sticky and form agglomerates during the ammoniation. What I claim is: v

1. A method of making an ammonium phosphate composition which comprises treating mono-ammonium phosphate in a substantially dry condition with ammonia.

29A method of making an ammonium phosphate composition which comprises treating mono-ammonium phos hate in a substantially dry condition wit ammonia and allowing the ammonia to remain in contact with the ammonium phosphate for an appreciable length of time.

3. A method of making an ammonium' phosphate composition :which comprises treating mono-ammonium phos hate in a substantially dry condition wit ammonia until the ammonia content of the composition exceeds 15%.

4. A method of making an ammonium phosphate composition which comprises treating mono-ammonium phosphate in a substantially dry condition with ammonia. at a temperature above atmospheric.

5. A method of making an ammonium phosphate composition which comprises treating mono-ammonium phosphate in a substantially dry condition with ammonia at a temperature above 60 C.

t contains in addition to" the 6. A method of making an ammonium phosphate" composition which comprises treating mono-ammonium phosphate in a substantially dry condition .with ammonia at a temperature between 60 and 150 C.

7. A method of making an ammonium phosphate composition -which comprises treating mono-ammonium phosphate in a substantially dry condition with ammonia at a temperature above atmospheric and at elevated pressure.

In testimony whereof, I have hereunto subscribed my name this 21 day of January,

GUY H. BUCHANAN. 

